Five-hundred-meter Aperture Spherical radio Telescope( FAST) is the largest sensitive single dish radio telescope in the world,in which the control and measurement of the feed is one crucial section of the FAST contro...Five-hundred-meter Aperture Spherical radio Telescope( FAST) is the largest sensitive single dish radio telescope in the world,in which the control and measurement of the feed is one crucial section of the FAST control system. Trilateration is presented to obtain three-dimensional coordinate for tracking feed focus cabin. Every three total stations chase prism movement to be attached on feed focus cabin and the prism position is determined from the measured distances based on the principle of trilateration. Therefore,feed position is determined from three prisms on the focus cabin. This study is to assess the accuracy and reliability of trilateration calculation on tracking focus cabin of FAST. Different arrangement of total stations on trilateration is theoretically studied. Through experiment,the proposed method shows that the accuracy is better than that of the polar coordinate measurement. The average root mean square error is lower than 0. 6 mm,which is found to have high accuracy and reliability.展开更多
"中国天眼"——500 m口径球面射电望远镜(Five hundred meter aperture spherical radio telescope,FAST)日前已投入使用,其独创的光机电一体化馈源支撑方案使得结构重量降低2个数量级。在6根柔索对馈源舱进行初步定位的基础..."中国天眼"——500 m口径球面射电望远镜(Five hundred meter aperture spherical radio telescope,FAST)日前已投入使用,其独创的光机电一体化馈源支撑方案使得结构重量降低2个数量级。在6根柔索对馈源舱进行初步定位的基础上,舱内的AB轴机构和精调Stewart平台支撑起馈源平台,并进行实时位姿补偿以实现馈源对天文目标的高精度跟踪。为避免通过各级驱动关节反馈值计算馈源平台位姿时,不能反映杆件弹性变形、铰链间隙引入的馈源平台误差,提出一种基于线驱动并联机构的馈源平台6自由度位姿直接测量方法,研究了测量系统的数学模型,利用机构构型的特点简化了线驱动并联机构的位姿正解算法。通过将简化后的位姿正解算法与传统6自由度机构位姿正解算法进行对比,验证了该方法的有效性和实时性;进一步分析了基于该方法的测量系统误差来源,得出了机构参数的误差映射关系。数值仿真结果表明:基于线驱动并联机构6自由度位姿测量系统具有误差平均效应,通过拉线连接点优化布局能够达到0.5 mm和0.025°的测量精度。展开更多
A fast tool servo (FTS) system is developed for the fabrication of non-rotationally symmetric micro-structured surfaces using single-point diamond turning machines.The constructed FTS employs a piezoelectric tube actu...A fast tool servo (FTS) system is developed for the fabrication of non-rotationally symmetric micro-structured surfaces using single-point diamond turning machines.The constructed FTS employs a piezoelectric tube actuator (PZT) to actuate the diamond tool and a capacitive probe as the feedback sensor.To compensate the inherent nonlinear hysteresis behavior of the piezoelectric actuator,Proportional Integral (PI) feedback control is implemented.Besides,a feed-forward control based on a simple feed-forward predictor has been added to achieve better tracking performance.Experimental results indicate that error motions in the performance of the system caused by hysteresis can be reduced greatly and the micro-structured surface is successfully fabricated by implementing the FTS.展开更多
Background: Previous studies have shown that ICU patients receive only a fraction of their calculated nutritional goals, and that cumulative caloric deficit in the ICU has been correlated with poor outcome. One reason...Background: Previous studies have shown that ICU patients receive only a fraction of their calculated nutritional goals, and that cumulative caloric deficit in the ICU has been correlated with poor outcome. One reason for this underfeeding is the frequent interruption of enteral nutrition. Many ICU patients receive enteral feeding formula via a nasogastric (NG) tube. Feeding is typically held for several hours prior to procedures due to the theoretical risk of aspiration. An alternative is to continue feeding up until the procedure begins, then stop the feeding and place the NG to suction. This evacuates the contents of the stomach and minimizes the risk of aspiration, while reducing the interruption of feeding that can result in malnutrition. Methods: This study is a review of prospectively gathered data including 55 sequential patients who underwent bedside percutaneous endoscopic gastrostomy (PEG) placement in a mixed ICU under a reduced fasting protocol. This was compared with a historical cohort of 33 critically ill trauma patients who fasted for at least 8 hours prior to the procedure. Under the reduced fasting protocol, enteral feeding via NG was continued up until the time of the procedure. The NG was then placed to suction, and sedation was given. The NG was left in place until the esophagus was cannulated, then it was removed. The PEG was placed in standard fashion, and feeding was resumed via the PEG immediately following the procedure. Results: We have documented no peri-procedural vomiting or aspiration. New diagnosis of pneumonia within 3 days occurred in 2/55 of the feeding group and 4/33 of the fasting group. Overall mortality was higher for the feeding group: 13/55 vs. 1/33, however when adjusted for baseline characteristics, the difference was no longer significant. Under our protocol, the interruption of feeding averaged approximately one hour, rather than the 8 or 9 hour interruption required by standard protocols. This saved an average of approximately 700 kilocalories per patient. Conclusion: We believe that continuing feeding via NG up until the time of bedside PEG is safe and advantageous for intubated patients in the ICU. Since there was minimal gastric content, it may also be safe for other procedures.展开更多
基金Supported by the National Natural Science Foundation of China(No.11273001,11373001,11703046)
文摘Five-hundred-meter Aperture Spherical radio Telescope( FAST) is the largest sensitive single dish radio telescope in the world,in which the control and measurement of the feed is one crucial section of the FAST control system. Trilateration is presented to obtain three-dimensional coordinate for tracking feed focus cabin. Every three total stations chase prism movement to be attached on feed focus cabin and the prism position is determined from the measured distances based on the principle of trilateration. Therefore,feed position is determined from three prisms on the focus cabin. This study is to assess the accuracy and reliability of trilateration calculation on tracking focus cabin of FAST. Different arrangement of total stations on trilateration is theoretically studied. Through experiment,the proposed method shows that the accuracy is better than that of the polar coordinate measurement. The average root mean square error is lower than 0. 6 mm,which is found to have high accuracy and reliability.
文摘"中国天眼"——500 m口径球面射电望远镜(Five hundred meter aperture spherical radio telescope,FAST)日前已投入使用,其独创的光机电一体化馈源支撑方案使得结构重量降低2个数量级。在6根柔索对馈源舱进行初步定位的基础上,舱内的AB轴机构和精调Stewart平台支撑起馈源平台,并进行实时位姿补偿以实现馈源对天文目标的高精度跟踪。为避免通过各级驱动关节反馈值计算馈源平台位姿时,不能反映杆件弹性变形、铰链间隙引入的馈源平台误差,提出一种基于线驱动并联机构的馈源平台6自由度位姿直接测量方法,研究了测量系统的数学模型,利用机构构型的特点简化了线驱动并联机构的位姿正解算法。通过将简化后的位姿正解算法与传统6自由度机构位姿正解算法进行对比,验证了该方法的有效性和实时性;进一步分析了基于该方法的测量系统误差来源,得出了机构参数的误差映射关系。数值仿真结果表明:基于线驱动并联机构6自由度位姿测量系统具有误差平均效应,通过拉线连接点优化布局能够达到0.5 mm和0.025°的测量精度。
基金Funded by the National High-tech R&D Program ("863" Program) of China (No.2006AA04Z314)
文摘A fast tool servo (FTS) system is developed for the fabrication of non-rotationally symmetric micro-structured surfaces using single-point diamond turning machines.The constructed FTS employs a piezoelectric tube actuator (PZT) to actuate the diamond tool and a capacitive probe as the feedback sensor.To compensate the inherent nonlinear hysteresis behavior of the piezoelectric actuator,Proportional Integral (PI) feedback control is implemented.Besides,a feed-forward control based on a simple feed-forward predictor has been added to achieve better tracking performance.Experimental results indicate that error motions in the performance of the system caused by hysteresis can be reduced greatly and the micro-structured surface is successfully fabricated by implementing the FTS.
文摘Background: Previous studies have shown that ICU patients receive only a fraction of their calculated nutritional goals, and that cumulative caloric deficit in the ICU has been correlated with poor outcome. One reason for this underfeeding is the frequent interruption of enteral nutrition. Many ICU patients receive enteral feeding formula via a nasogastric (NG) tube. Feeding is typically held for several hours prior to procedures due to the theoretical risk of aspiration. An alternative is to continue feeding up until the procedure begins, then stop the feeding and place the NG to suction. This evacuates the contents of the stomach and minimizes the risk of aspiration, while reducing the interruption of feeding that can result in malnutrition. Methods: This study is a review of prospectively gathered data including 55 sequential patients who underwent bedside percutaneous endoscopic gastrostomy (PEG) placement in a mixed ICU under a reduced fasting protocol. This was compared with a historical cohort of 33 critically ill trauma patients who fasted for at least 8 hours prior to the procedure. Under the reduced fasting protocol, enteral feeding via NG was continued up until the time of the procedure. The NG was then placed to suction, and sedation was given. The NG was left in place until the esophagus was cannulated, then it was removed. The PEG was placed in standard fashion, and feeding was resumed via the PEG immediately following the procedure. Results: We have documented no peri-procedural vomiting or aspiration. New diagnosis of pneumonia within 3 days occurred in 2/55 of the feeding group and 4/33 of the fasting group. Overall mortality was higher for the feeding group: 13/55 vs. 1/33, however when adjusted for baseline characteristics, the difference was no longer significant. Under our protocol, the interruption of feeding averaged approximately one hour, rather than the 8 or 9 hour interruption required by standard protocols. This saved an average of approximately 700 kilocalories per patient. Conclusion: We believe that continuing feeding via NG up until the time of bedside PEG is safe and advantageous for intubated patients in the ICU. Since there was minimal gastric content, it may also be safe for other procedures.
