The dynamics analysis plays an important role for the control, simulation and optimization of the parallel manipulators. Normally, the Stewart type manipulators have a platform and several legs. The inverse dynamics c...The dynamics analysis plays an important role for the control, simulation and optimization of the parallel manipulators. Normally, the Stewart type manipulators have a platform and several legs. The inverse dynamics can be solved efficiently by taking the advantage of such structural characteristics. However, for the forward dynamics analysis, this structural decomposition still faces challenges from both modeling and computation. In this paper, an efficient approach is proposed for the forward dynamics of the 6-PUS manipulator based on the platform-legs composite simulation. By composite method, the dynamics modeling of the parallel manipulator is separated into the forward dynamics of the platform and the kineto-statics of the legs. The global simulation model can be constructed by connecting the predefined platform model and leg models according to the manipulator＇s topology. Thus, the global simulation can be decomposed into the independent calculations of purely algebraic equations and ordinary differential equations （ODEs）, the computational cost can be reduced and the stability of the simulation can be improved. For the purpose of solving the manipulator＇s forward dynamics accurately, the algebraic-loop problem is discussed and a closed form algorithm is proposed. A numerical example of the 6-PUS manipulator is given to demonstrate the effectiveness of the proposed approach. The example results show that the modeling efficiency can be improved and the simulation stability can be ensured for decomposing the system equations into purely algebraic equations and ODEs.展开更多
Most researches focused on the analytical stabilized algorithm for the modular simulation of single domain, e.g., pure mechanical systems. Only little work has been performed on the problem of multi-domain simulation ...Most researches focused on the analytical stabilized algorithm for the modular simulation of single domain, e.g., pure mechanical systems. Only little work has been performed on the problem of multi-domain simulation stability influenced by algebraic loops. In this paper, the algebraic loop problem is studied by a composite simulation method to reveal the internal relationship between simulation stability and system topologies and simulation unit models. A stability criterion of multi-domain composite simulation is established, and two algebraic loop compensation algorithms are proposed using numerical iteration and approximate function in multi-domain simulation. The numerical stabilized algorithm is the Newton method for the solution of the set of nonlinear equations, and it is used here in simulation of the system composed of mechanical system and hydraulic system. The approximate stabilized algorithm is the construction of response surface for inputs and outputs of unknown unit model, and it is utilized here in simulation of the system composed of forging system, mechanical and hydraulic system. The effectiveness of the algorithms is verified by a case study of multi-domain simulation for forging system composed of thermoplastic deformation of workpieces, mechanical system and hydraulic system of a manipulator. The system dynamics simulation results show that curves of motion and force are continuous and convergent. This paper presents two algorithms, which are applied to virtual reality simulation of forging process in a simulation platform for a manipulator, and play a key role in simulation efficiency and stability.展开更多
The mechanism type plays a decisive role in the mechanical performance of robotic manipulators. Feasible mechanism types can be obtained by applying appropriate type synthesis theory, but there is still a lack of effe...The mechanism type plays a decisive role in the mechanical performance of robotic manipulators. Feasible mechanism types can be obtained by applying appropriate type synthesis theory, but there is still a lack of effective and efficient methods for the optimum selection among different types of mechanism candidates. This paper presents a new strategy for the purpose of optimum mechanism type selection based on the modified particle swarm optimization method. The concept of sub-swarm is introduced to represent the different mechanisms generated by the type synthesis, and a competitive mechanism is employed between the sub-swarms to reassign their population size according to the relative performances of the mechanism candidates to implement the optimization. Combining with a modular modeling approach for fast calculation of the performance index of the potential candidates, the proposed method is applied to determine the optimum mechanism type among the potential candidates for the desired manipulator. The effectiveness and efficiency of the proposed method is demonstrated through a case study on the optimum selection of mechanism type of a heavy manipulator where six feasible candidates are considered with force capability as the specific performance index. The optimization result shows that the fitness of the optimum mechanism type for the considered heavy manipulator can be up to 0.578 5. This research provides the instruction in optimum selection of mechanism types for robotic manipulators.展开更多
A simple and reliable contact algorithm for staticimplicit FE code is proposed.It can overcome miss-judgement and error-judgement, and improve convergence effectively, and can apply friction boundary condition conveni...A simple and reliable contact algorithm for staticimplicit FE code is proposed.It can overcome miss-judgement and error-judgement, and improve convergence effectively, and can apply friction boundary condition conveniently. Based on the proposed contact algorithm,some typical sheet metal forming processes and one benchmark of NUMISHEET 93 are simulated by static-implicit FE code developed by the authors and their group.展开更多
As the most important performance,compliance of shield tunneling machines(STM) is defined as the capability to accommodate the sudden change of the load induced by the variable geological conditions during excavation....As the most important performance,compliance of shield tunneling machines(STM) is defined as the capability to accommodate the sudden change of the load induced by the variable geological conditions during excavation.Owing to the different requirements of the compliant tasks,the existing methods in the robotic field cannot be utilized in the analysis and design of the mechanical system of shield tunneling machines.In this paper,based on the stiffness of the mechanical system and the equivalent contact stiffness of the tunnel face,the tunneling interface-matching index(IMI) is proposed to evaluate the compliance of the machine.The IMI is defined as a metric to describe the coincidence of the stiffness curves of the mechanical system and the tunnel face.Moreover,a tunneling case is investigated in the paper as an example to expound the validation of IMI and the analytical process.In conclusion,the IMI presented here can be served as an appraisement of the capability in conforming to the load fluctuation,and give instructions for the design of the thrust system of shield tunneling machines.展开更多
This paper presents a composite modeling method of the forward dynamics in general planar mechanical system. In the modeling process, the system dynamic model is generated by assembling the model units which are kinem...This paper presents a composite modeling method of the forward dynamics in general planar mechanical system. In the modeling process, the system dynamic model is generated by assembling the model units which are kinematical determinate in planar mechanisms rather than the body/joint units in multi-body system. A state space formulation is employed to model both the unit and system models. The validation and feasibility of the method are illustrated by a case study of a four-bar mechanism. The advantage of this method is that the models are easier to reuse and the system is easier to reconfigure. The formulation reveals the relationship between the topology and dynamics of the planar mechanism to some extent.展开更多
基金supported by National Natural Science Foundation of China (Grant No. 50605042)National Basic Research Program of China (973 Program, Grant No. 2006CB705400)
文摘The dynamics analysis plays an important role for the control, simulation and optimization of the parallel manipulators. Normally, the Stewart type manipulators have a platform and several legs. The inverse dynamics can be solved efficiently by taking the advantage of such structural characteristics. However, for the forward dynamics analysis, this structural decomposition still faces challenges from both modeling and computation. In this paper, an efficient approach is proposed for the forward dynamics of the 6-PUS manipulator based on the platform-legs composite simulation. By composite method, the dynamics modeling of the parallel manipulator is separated into the forward dynamics of the platform and the kineto-statics of the legs. The global simulation model can be constructed by connecting the predefined platform model and leg models according to the manipulator＇s topology. Thus, the global simulation can be decomposed into the independent calculations of purely algebraic equations and ordinary differential equations （ODEs）, the computational cost can be reduced and the stability of the simulation can be improved. For the purpose of solving the manipulator＇s forward dynamics accurately, the algebraic-loop problem is discussed and a closed form algorithm is proposed. A numerical example of the 6-PUS manipulator is given to demonstrate the effectiveness of the proposed approach. The example results show that the modeling efficiency can be improved and the simulation stability can be ensured for decomposing the system equations into purely algebraic equations and ODEs.
基金supported by National Natural Science Foundation of China(Grant Nos.51075259,51121063,51305256)National Basic Research Program of China(973 Program,Grant No.2006CB705400)
文摘Most researches focused on the analytical stabilized algorithm for the modular simulation of single domain, e.g., pure mechanical systems. Only little work has been performed on the problem of multi-domain simulation stability influenced by algebraic loops. In this paper, the algebraic loop problem is studied by a composite simulation method to reveal the internal relationship between simulation stability and system topologies and simulation unit models. A stability criterion of multi-domain composite simulation is established, and two algebraic loop compensation algorithms are proposed using numerical iteration and approximate function in multi-domain simulation. The numerical stabilized algorithm is the Newton method for the solution of the set of nonlinear equations, and it is used here in simulation of the system composed of mechanical system and hydraulic system. The approximate stabilized algorithm is the construction of response surface for inputs and outputs of unknown unit model, and it is utilized here in simulation of the system composed of forging system, mechanical and hydraulic system. The effectiveness of the algorithms is verified by a case study of multi-domain simulation for forging system composed of thermoplastic deformation of workpieces, mechanical system and hydraulic system of a manipulator. The system dynamics simulation results show that curves of motion and force are continuous and convergent. This paper presents two algorithms, which are applied to virtual reality simulation of forging process in a simulation platform for a manipulator, and play a key role in simulation efficiency and stability.
基金supported by National Natural Science Foundation of China (Grant No. 51075259)Program for New Century Excellent Talents in University of Ministry of Education, China (Grant No. NCET-10-0579)+1 种基金National Basic Research Program of China (973 program, Grant No.2006CB705407)Key Technologies R&D Program of Shanghai,China (Grant No. 10111100203)
文摘The mechanism type plays a decisive role in the mechanical performance of robotic manipulators. Feasible mechanism types can be obtained by applying appropriate type synthesis theory, but there is still a lack of effective and efficient methods for the optimum selection among different types of mechanism candidates. This paper presents a new strategy for the purpose of optimum mechanism type selection based on the modified particle swarm optimization method. The concept of sub-swarm is introduced to represent the different mechanisms generated by the type synthesis, and a competitive mechanism is employed between the sub-swarms to reassign their population size according to the relative performances of the mechanism candidates to implement the optimization. Combining with a modular modeling approach for fast calculation of the performance index of the potential candidates, the proposed method is applied to determine the optimum mechanism type among the potential candidates for the desired manipulator. The effectiveness and efficiency of the proposed method is demonstrated through a case study on the optimum selection of mechanism type of a heavy manipulator where six feasible candidates are considered with force capability as the specific performance index. The optimization result shows that the fitness of the optimum mechanism type for the considered heavy manipulator can be up to 0.578 5. This research provides the instruction in optimum selection of mechanism types for robotic manipulators.
基金This project is supported by Shanghai Automotive Foundation.
文摘A simple and reliable contact algorithm for staticimplicit FE code is proposed.It can overcome miss-judgement and error-judgement, and improve convergence effectively, and can apply friction boundary condition conveniently. Based on the proposed contact algorithm,some typical sheet metal forming processes and one benchmark of NUMISHEET 93 are simulated by static-implicit FE code developed by the authors and their group.
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2007CB714003)the National Natural Science Foundation of China (Grant Nos. 51075259 and 50905108)the Program for New Century Excellent Talents in University (Grant No.NCET-10-0579)
文摘As the most important performance,compliance of shield tunneling machines(STM) is defined as the capability to accommodate the sudden change of the load induced by the variable geological conditions during excavation.Owing to the different requirements of the compliant tasks,the existing methods in the robotic field cannot be utilized in the analysis and design of the mechanical system of shield tunneling machines.In this paper,based on the stiffness of the mechanical system and the equivalent contact stiffness of the tunnel face,the tunneling interface-matching index(IMI) is proposed to evaluate the compliance of the machine.The IMI is defined as a metric to describe the coincidence of the stiffness curves of the mechanical system and the tunnel face.Moreover,a tunneling case is investigated in the paper as an example to expound the validation of IMI and the analytical process.In conclusion,the IMI presented here can be served as an appraisement of the capability in conforming to the load fluctuation,and give instructions for the design of the thrust system of shield tunneling machines.
基金the National Natural Science Foundation of China (Grant No. 50605042)the National Basic Research Program of China (973 Program) (Grant No. 2006CB705400)
文摘This paper presents a composite modeling method of the forward dynamics in general planar mechanical system. In the modeling process, the system dynamic model is generated by assembling the model units which are kinematical determinate in planar mechanisms rather than the body/joint units in multi-body system. A state space formulation is employed to model both the unit and system models. The validation and feasibility of the method are illustrated by a case study of a four-bar mechanism. The advantage of this method is that the models are easier to reuse and the system is easier to reconfigure. The formulation reveals the relationship between the topology and dynamics of the planar mechanism to some extent.
