In the process of tunnel construction, the removal of the middle partition wall will affect the stability of the structure. This study compares and selects the spacing of I-beam as temporary support after the removal ...In the process of tunnel construction, the removal of the middle partition wall will affect the stability of the structure. This study compares and selects the spacing of I-beam as temporary support after the removal of the middle partition wall in shilao section. Two schemes with I-beam spacing of 1m and 2m are selected respectively. The surface settlement value and vault settlement value of the two schemes are analyzed, and finally a reasonable I-beam support spacing scheme is determined. The results show that the spacing of I-beam under the two schemes meets the requirements. However, from an economic point of view, on the premise that both schemes meet the requirements, scheme 2 should be selected, that is, the I-steel double support spacing is 2m, which can not only save the cost, but also meet the safety requirements of construction.展开更多
The development of new robot structures, in particular of parallel kinematic machines（PKM）, is widely systematized by different structure synthesis methods. Recent research increasingly focuses on PKM with less than...The development of new robot structures, in particular of parallel kinematic machines（PKM）, is widely systematized by different structure synthesis methods. Recent research increasingly focuses on PKM with less than six degrees of freedom（DOF）. However, an overall comparison and evaluation of these structures is missing. In order to compare symmetrical PKM with three translational DOF, different evaluation criteria are used. Workspace, maximum actuation forces and velocities, power, actuator stiffness, accuracy and transmission behavior are taken into account to investigate strengths and weaknesses of the PKMs. A selection scheme based on possible configurations of translational PKM including different frame configurations is presented. Moreover, an optimization method based on a genetic algorithm is described to determine the geometric parameters of the selected PKM for an exemplary load case and a prescribed workspace. The values of the mentioned criteria are determined for all considered PKM with respect to certain boundary conditions. The distribution and spreading of these values within the prescribed workspace is presented by using box plots for each criterion. Thereby, the performance characteristics of the different structures can be compared directly. The results show that there is no ＂best＂ PKM. Further inquiries such as dynamic or stiffness analysis are necessary to extend the comparison and to finally select a PKM.展开更多
文摘In the process of tunnel construction, the removal of the middle partition wall will affect the stability of the structure. This study compares and selects the spacing of I-beam as temporary support after the removal of the middle partition wall in shilao section. Two schemes with I-beam spacing of 1m and 2m are selected respectively. The surface settlement value and vault settlement value of the two schemes are analyzed, and finally a reasonable I-beam support spacing scheme is determined. The results show that the spacing of I-beam under the two schemes meets the requirements. However, from an economic point of view, on the premise that both schemes meet the requirements, scheme 2 should be selected, that is, the I-steel double support spacing is 2m, which can not only save the cost, but also meet the safety requirements of construction.
文摘The development of new robot structures, in particular of parallel kinematic machines（PKM）, is widely systematized by different structure synthesis methods. Recent research increasingly focuses on PKM with less than six degrees of freedom（DOF）. However, an overall comparison and evaluation of these structures is missing. In order to compare symmetrical PKM with three translational DOF, different evaluation criteria are used. Workspace, maximum actuation forces and velocities, power, actuator stiffness, accuracy and transmission behavior are taken into account to investigate strengths and weaknesses of the PKMs. A selection scheme based on possible configurations of translational PKM including different frame configurations is presented. Moreover, an optimization method based on a genetic algorithm is described to determine the geometric parameters of the selected PKM for an exemplary load case and a prescribed workspace. The values of the mentioned criteria are determined for all considered PKM with respect to certain boundary conditions. The distribution and spreading of these values within the prescribed workspace is presented by using box plots for each criterion. Thereby, the performance characteristics of the different structures can be compared directly. The results show that there is no ＂best＂ PKM. Further inquiries such as dynamic or stiffness analysis are necessary to extend the comparison and to finally select a PKM.
