Externally pressurized spherical air bearings are the key component of the three-axis air bearing table, and the manufacturing errors of the bearing affects the performance of the air bearing table. However, the manuf...Externally pressurized spherical air bearings are the key component of the three-axis air bearing table, and the manufacturing errors of the bearing affects the performance of the air bearing table. However, the manufacturing errors are unavoidable, and the pursuit to enhance the manufacturing accuracy will increase the cost greatly. In order to provide some theoretical guideline for the tolerance choice in the design of the externally pressurized spherical air bearings with inherent compensation, the effects of several manufacturing errors on the static characteristics of the air bearing are studied. Due to the complex geometry of the computational domain, an unstructured meshing technology is used for mesh generation. A finite-volume method is adopted to discretize the three-dimensional steady-state compressible Navier-Stokes equations. A modified SIMPLE algorithm which is suitable for compressible flows is applied to solve the discretized governing equations. The effects of the dimension error and the roundness error of the ball head and the ball socket on the static characteristics are investigated. The investigation result shows that the positive dimension error and the oblate spheroid-type roundness error of the ball head as well as the negative dimension error and the prolate spheroid-type roundness error of the ball socket can improve the bearing capacity and static stiffness of the air bearings by reducing the mass flow. The calculation method proposed in this paper fits well for the general principle, which can be extended to the characteristics analysis of other air bearings.展开更多
The filling and exhausting processes in a pneumatic system are involved with many factors, and numerical solutions of many partial differential equations are always adapted in the study of those processes, which have ...The filling and exhausting processes in a pneumatic system are involved with many factors, and numerical solutions of many partial differential equations are always adapted in the study of those processes, which have been proved to be troublesome and less intuitive. Analytical solutions based on loss-less tube model and average friction tube model are found respectively by using fluid net theory, and they fit the experimental results well. The research work shows that： Fluid net theory can be used to solve the analytical solution of filling and exhausting processes of pneumatic system, and the result of loss-less tube model is close to that of average friction model, so loss-less tube model is recommended since it is simpler, and the difference between filling time and exhausting time is determined by initial and final pressures, the volume of container and the section area of tube, and has nothing to do with the length of the tube.展开更多
目的:探讨经右胸全胸腔镜下体外循环停跳下心房粘液瘤切除术的可行性,评价其临床安全性及应用价值。方法:回顾性分析2011年12月至2018年12月,重庆市人民医院(中国科学院大学重庆医院)接受完全胸腔镜下心脏粘液瘤切除术的患者32例,其中,...目的:探讨经右胸全胸腔镜下体外循环停跳下心房粘液瘤切除术的可行性,评价其临床安全性及应用价值。方法:回顾性分析2011年12月至2018年12月,重庆市人民医院(中国科学院大学重庆医院)接受完全胸腔镜下心脏粘液瘤切除术的患者32例,其中,左心房粘液瘤30例,右心房粘液瘤2例,男14例,女18例。术前心功能分级(New York Heart Association,NYHA),Ⅰ级8例,Ⅱ级17例,Ⅲ级7例。股动静脉插管、右颈内静脉插管引流建立体外循环,全胸腔镜下经右胸副操作孔阻断升主动脉,心脏停跳后经右心房和房间隔入路行粘液瘤切除。结果:无围术期死亡,手术时间[(176.13±8.12)min],体外循环时间[(132.19±6.45)min],主动脉阻断时间[(70.94±3.80)min]。术后48h出血量[(283.71±44.28)mL];10例患者术中输血,输血率31.25%;中位输血量2(0,4)u。术中行食道超声检查及出院前复查心脏超声,心脏粘液瘤均完整切除,无残余心脏粘液瘤。各瓣膜功能良好。目前随访期间患者无再发心脏粘液瘤,无心脏瓣膜疾病再次心脏手术,无严重心脑血管并发症。结论:体外循环下经右胸全胸腔镜下行心房粘液瘤切除安全可行,其临床疗效确切,且手术创伤和术后瘢痕更小,利于术后患者恢复。展开更多
A newly designed pneumatic spring with two separate chambers is promoted and double-loop active control is introduced to overcome the following drawbacks of passive pneumatic isolation： ① The low frequency resonance...A newly designed pneumatic spring with two separate chambers is promoted and double-loop active control is introduced to overcome the following drawbacks of passive pneumatic isolation： ① The low frequency resonances introduced into the system; ② Conflict between lower isolation frequency and stiffness high enough to limit quasi-static stroke;③ Inconsistent isolation level with different force load. The design of two separate chambers is for the purpose of tuning support frequency and force independently and each chamber is controlled by a different valve. The inner one of double-loop structure is pressure control, and in order to obtain good performance, nonlinearities compensation and motion flow rate compensation （MFRC） are added besides the basic cascade compensation, and the influence of tube length is studied. The outer loop has two functions： one is to eliminate the resonance caused by isolation support and to broaden the isolation frequency band by payload velocity feedback and base velocity feed forward, and the other is to tune support force and support stiffness simultaneously and independently, which means the support force will have no effect on support stiffness. Theoretical analysis and experiment results show that the three drawbacks are overcome simultaneously.展开更多
基金supported by National Natural Science Foundation ofChina (Grant No. 50335010)
文摘Externally pressurized spherical air bearings are the key component of the three-axis air bearing table, and the manufacturing errors of the bearing affects the performance of the air bearing table. However, the manufacturing errors are unavoidable, and the pursuit to enhance the manufacturing accuracy will increase the cost greatly. In order to provide some theoretical guideline for the tolerance choice in the design of the externally pressurized spherical air bearings with inherent compensation, the effects of several manufacturing errors on the static characteristics of the air bearing are studied. Due to the complex geometry of the computational domain, an unstructured meshing technology is used for mesh generation. A finite-volume method is adopted to discretize the three-dimensional steady-state compressible Navier-Stokes equations. A modified SIMPLE algorithm which is suitable for compressible flows is applied to solve the discretized governing equations. The effects of the dimension error and the roundness error of the ball head and the ball socket on the static characteristics are investigated. The investigation result shows that the positive dimension error and the oblate spheroid-type roundness error of the ball head as well as the negative dimension error and the prolate spheroid-type roundness error of the ball socket can improve the bearing capacity and static stiffness of the air bearings by reducing the mass flow. The calculation method proposed in this paper fits well for the general principle, which can be extended to the characteristics analysis of other air bearings.
基金This project is supported by National Natural Science Foundation of China(No.50575209).
文摘The filling and exhausting processes in a pneumatic system are involved with many factors, and numerical solutions of many partial differential equations are always adapted in the study of those processes, which have been proved to be troublesome and less intuitive. Analytical solutions based on loss-less tube model and average friction tube model are found respectively by using fluid net theory, and they fit the experimental results well. The research work shows that： Fluid net theory can be used to solve the analytical solution of filling and exhausting processes of pneumatic system, and the result of loss-less tube model is close to that of average friction model, so loss-less tube model is recommended since it is simpler, and the difference between filling time and exhausting time is determined by initial and final pressures, the volume of container and the section area of tube, and has nothing to do with the length of the tube.
文摘目的:探讨经右胸全胸腔镜下体外循环停跳下心房粘液瘤切除术的可行性,评价其临床安全性及应用价值。方法:回顾性分析2011年12月至2018年12月,重庆市人民医院(中国科学院大学重庆医院)接受完全胸腔镜下心脏粘液瘤切除术的患者32例,其中,左心房粘液瘤30例,右心房粘液瘤2例,男14例,女18例。术前心功能分级(New York Heart Association,NYHA),Ⅰ级8例,Ⅱ级17例,Ⅲ级7例。股动静脉插管、右颈内静脉插管引流建立体外循环,全胸腔镜下经右胸副操作孔阻断升主动脉,心脏停跳后经右心房和房间隔入路行粘液瘤切除。结果:无围术期死亡,手术时间[(176.13±8.12)min],体外循环时间[(132.19±6.45)min],主动脉阻断时间[(70.94±3.80)min]。术后48h出血量[(283.71±44.28)mL];10例患者术中输血,输血率31.25%;中位输血量2(0,4)u。术中行食道超声检查及出院前复查心脏超声,心脏粘液瘤均完整切除,无残余心脏粘液瘤。各瓣膜功能良好。目前随访期间患者无再发心脏粘液瘤,无心脏瓣膜疾病再次心脏手术,无严重心脑血管并发症。结论:体外循环下经右胸全胸腔镜下行心房粘液瘤切除安全可行,其临床疗效确切,且手术创伤和术后瘢痕更小,利于术后患者恢复。
基金This project is supported by Commission of Science Technology and Industry for National Defense, China.
文摘A newly designed pneumatic spring with two separate chambers is promoted and double-loop active control is introduced to overcome the following drawbacks of passive pneumatic isolation： ① The low frequency resonances introduced into the system; ② Conflict between lower isolation frequency and stiffness high enough to limit quasi-static stroke;③ Inconsistent isolation level with different force load. The design of two separate chambers is for the purpose of tuning support frequency and force independently and each chamber is controlled by a different valve. The inner one of double-loop structure is pressure control, and in order to obtain good performance, nonlinearities compensation and motion flow rate compensation （MFRC） are added besides the basic cascade compensation, and the influence of tube length is studied. The outer loop has two functions： one is to eliminate the resonance caused by isolation support and to broaden the isolation frequency band by payload velocity feedback and base velocity feed forward, and the other is to tune support force and support stiffness simultaneously and independently, which means the support force will have no effect on support stiffness. Theoretical analysis and experiment results show that the three drawbacks are overcome simultaneously.
