Line configuration and balancing is to select the type of line and allot a given set of operations as well as machines to a sequence of workstations to realize high-efficiency production. Most of the current researche...Line configuration and balancing is to select the type of line and allot a given set of operations as well as machines to a sequence of workstations to realize high-efficiency production. Most of the current researches for machining line configuration and balancing problems are related to dedicated transfer lines with dedicated machine workstations. With growing trends towards great product variety and fluctuations in market demand, dedicated transfer lines are being replaced with flexible machining line composed of identical CNC machines. This paper deals with the line configuration and balancing problem for flexible machining lines. The objective is to assign operations to workstations and find the sequence of execution, specify the number of machines in each workstation while minimizing the line cycle time and total number of machines. This problem is subject to precedence, clustering, accessibility and capacity constraints among the features, operations, setups and workstations. The mathematical model and heuristic algorithm based on feature group strategy and polychromatic sets theory are presented to find an optimal solution. The feature group strategy and polychromatic sets theory are used to establish constraint model. A heuristic operations sequencing and assignment algorithm is given. An industrial case study is carried out, and multiple optimal solutions in different line configurations are obtained. The case studying results show that the solutions with shorter cycle time and higher line balancing rate demonstrate the feasibility and effectiveness of the proposed algorithm. This research proposes a heuristic line configuration and balancing algorithm based on feature group strategy and polychromatic sets theory which is able to provide better solutions while achieving an improvement in computing time.展开更多
This paper explores multi-impulse trajectory design for approaching Geostationary Earth Orbit(GEO)targets,emphasizing the attainment of a 2:1 elliptical relative orbit for close inspection.The intricate optimization c...This paper explores multi-impulse trajectory design for approaching Geostationary Earth Orbit(GEO)targets,emphasizing the attainment of a 2:1 elliptical relative orbit for close inspection.The intricate optimization challenge includes dynamic and terminal constraints,as well as total mission duration limitations.Critical variables like transfer duration,impulse count,timing,and entry point are optimized using genetic algorithms to minimize velocity increment requirements.These optimal values are influenced by uncertain terminal states constrained by the 2:1 circling orbit.To address these complexities,the paper leverages a linear state transition matrix from relative orbital dynamics to formulate a multi-impulse optimization model.Additionally,a differential correction-based iterative approach mitigates nonlinear dynamics’impact on terminal rendezvous errors.Through theoretical analysis and simulations,the study elucidates variations in optimization criteria,particularly in GEO missions with multiple impulses,and identifies optimal entry points for different impulse counts.The proposed models and methodologies offer theoretical insights for future GEO orbit approaching missions and potential applications in various space maneuver tasks.展开更多
基金Supported by Shanghai Municipal Science and Technology Commission(Grant No.12JC1408700)National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant Nos.2013ZX04012-071,2011ZX04015-022)
文摘Line configuration and balancing is to select the type of line and allot a given set of operations as well as machines to a sequence of workstations to realize high-efficiency production. Most of the current researches for machining line configuration and balancing problems are related to dedicated transfer lines with dedicated machine workstations. With growing trends towards great product variety and fluctuations in market demand, dedicated transfer lines are being replaced with flexible machining line composed of identical CNC machines. This paper deals with the line configuration and balancing problem for flexible machining lines. The objective is to assign operations to workstations and find the sequence of execution, specify the number of machines in each workstation while minimizing the line cycle time and total number of machines. This problem is subject to precedence, clustering, accessibility and capacity constraints among the features, operations, setups and workstations. The mathematical model and heuristic algorithm based on feature group strategy and polychromatic sets theory are presented to find an optimal solution. The feature group strategy and polychromatic sets theory are used to establish constraint model. A heuristic operations sequencing and assignment algorithm is given. An industrial case study is carried out, and multiple optimal solutions in different line configurations are obtained. The case studying results show that the solutions with shorter cycle time and higher line balancing rate demonstrate the feasibility and effectiveness of the proposed algorithm. This research proposes a heuristic line configuration and balancing algorithm based on feature group strategy and polychromatic sets theory which is able to provide better solutions while achieving an improvement in computing time.
基金supported by the National Natural Science Foundation of China(grant number 12172288)the National Key Basic Research Program of China:Gravitational Wave Detection Project(grant numbers 2021YFC2202601 and 2021YFC2202603).
文摘This paper explores multi-impulse trajectory design for approaching Geostationary Earth Orbit(GEO)targets,emphasizing the attainment of a 2:1 elliptical relative orbit for close inspection.The intricate optimization challenge includes dynamic and terminal constraints,as well as total mission duration limitations.Critical variables like transfer duration,impulse count,timing,and entry point are optimized using genetic algorithms to minimize velocity increment requirements.These optimal values are influenced by uncertain terminal states constrained by the 2:1 circling orbit.To address these complexities,the paper leverages a linear state transition matrix from relative orbital dynamics to formulate a multi-impulse optimization model.Additionally,a differential correction-based iterative approach mitigates nonlinear dynamics’impact on terminal rendezvous errors.Through theoretical analysis and simulations,the study elucidates variations in optimization criteria,particularly in GEO missions with multiple impulses,and identifies optimal entry points for different impulse counts.The proposed models and methodologies offer theoretical insights for future GEO orbit approaching missions and potential applications in various space maneuver tasks.
