Scanning probe microscopes (SPM) are limited in their speed of data acquisition by the mechanical stability of the scanner. Therefore many types of scanners have been developed to achieve a rigid setup while maintaini...Scanning probe microscopes (SPM) are limited in their speed of data acquisition by the mechanical stability of the scanner. Therefore many types of scanners have been developed to achieve a rigid setup while maintaining an acceptable image size. We have followed here a different path to accelerate data acquisition by improving the feedback loop to achieve the same SPM image quality in a shorter time. While the feedback loop in a scanning probe microscope typically starts to probe a new pixel starting from the previous position, we have reduced the total control time by using an improved starting point for the feedback loop at each pixel. By exploiting the information of the already scanned pixels a forecast for the new pixel is created. We have successfully used several simple methods for a prognosis in MATLAB simulations like one dimensional linear or cubic extrapolation and others. Only scanning tunnelling microscope data from real experiments were used to test the forecasts. A doubling of the speed was achieved in the most favourable cases.展开更多
This paper focuses on the H∞ controller design for linear systems with time-varying delays and norm-bounded parameter perturbations in the system state and control/disturbance. On the existence of delayed/undelayed f...This paper focuses on the H∞ controller design for linear systems with time-varying delays and norm-bounded parameter perturbations in the system state and control/disturbance. On the existence of delayed/undelayed full state feedback controllers, we present a sufficient condition and give a design method in the form of Riccati equation. The controller can not only stabilize the time-delay system, but also make the H∞ norm of the closed-loop system be less than a given bound. This result practically generalizes the related results in current literature.展开更多
The effectiveness of the magnetic confinement of plasma can be improved by elongat- ing the plasma cross-section in tokamak devices. But elongated plasma has vertical displacement instability, so a feedback control sy...The effectiveness of the magnetic confinement of plasma can be improved by elongat- ing the plasma cross-section in tokamak devices. But elongated plasma has vertical displacement instability, so a feedback control system is needed to restrain the plasma＇s vertical displacement. A fast control power supply is needed to excite the active feedback coils, which produces a magnetic field to control the plasma＇s displacement. With the development of EAST, the fast control power supply needs to keep on enhancing the fast response and output current. The structure of a new power supply is introduced in this paper. The method of multiple inverters paralleled with the current sharing reactor is presented to meet the need for large current and fast control. According to the design demands of the EAST fast control power supply, the adjuster of the current close loop is applied to the inverter, which can advance its ability to restrain the loop current in low frequency and DC output. The result of the experiment confirms the validity of the proposed scheme and control strategy.展开更多
The non-minimum phase feature of tail-controlled missile airframes is analyzed. Three selection strategies for desired performance indexes are presented. An acceleration autopilot design methodology based on output fe...The non-minimum phase feature of tail-controlled missile airframes is analyzed. Three selection strategies for desired performance indexes are presented. An acceleration autopilot design methodology based on output feedback and optimization is proposed. Performance and robustness comparisons between the two-loop and classical three-loop topologies are made. Attempts to improve the classical three-loop topology are discussed. Despite the same open-loop structure, the classical three-loop autopilot shows distinct characteristics from a two-loop autopilot with PI compensator. Both the two-loop and three-loop topologies can stabilize a static unstable missile. However, the finite actuator resource is the crucial factor dominating autopilot function.展开更多
文摘Scanning probe microscopes (SPM) are limited in their speed of data acquisition by the mechanical stability of the scanner. Therefore many types of scanners have been developed to achieve a rigid setup while maintaining an acceptable image size. We have followed here a different path to accelerate data acquisition by improving the feedback loop to achieve the same SPM image quality in a shorter time. While the feedback loop in a scanning probe microscope typically starts to probe a new pixel starting from the previous position, we have reduced the total control time by using an improved starting point for the feedback loop at each pixel. By exploiting the information of the already scanned pixels a forecast for the new pixel is created. We have successfully used several simple methods for a prognosis in MATLAB simulations like one dimensional linear or cubic extrapolation and others. Only scanning tunnelling microscope data from real experiments were used to test the forecasts. A doubling of the speed was achieved in the most favourable cases.
基金This project was supported by the National Natural Science Foundation of China (No. 69974022).
文摘This paper focuses on the H∞ controller design for linear systems with time-varying delays and norm-bounded parameter perturbations in the system state and control/disturbance. On the existence of delayed/undelayed full state feedback controllers, we present a sufficient condition and give a design method in the form of Riccati equation. The controller can not only stabilize the time-delay system, but also make the H∞ norm of the closed-loop system be less than a given bound. This result practically generalizes the related results in current literature.
基金supported in part by the ITER Program of China(973 Program)(No.2011GB109002)National Natural Science Foundation of China(No.11275056)
文摘The effectiveness of the magnetic confinement of plasma can be improved by elongat- ing the plasma cross-section in tokamak devices. But elongated plasma has vertical displacement instability, so a feedback control system is needed to restrain the plasma＇s vertical displacement. A fast control power supply is needed to excite the active feedback coils, which produces a magnetic field to control the plasma＇s displacement. With the development of EAST, the fast control power supply needs to keep on enhancing the fast response and output current. The structure of a new power supply is introduced in this paper. The method of multiple inverters paralleled with the current sharing reactor is presented to meet the need for large current and fast control. According to the design demands of the EAST fast control power supply, the adjuster of the current close loop is applied to the inverter, which can advance its ability to restrain the loop current in low frequency and DC output. The result of the experiment confirms the validity of the proposed scheme and control strategy.
文摘The non-minimum phase feature of tail-controlled missile airframes is analyzed. Three selection strategies for desired performance indexes are presented. An acceleration autopilot design methodology based on output feedback and optimization is proposed. Performance and robustness comparisons between the two-loop and classical three-loop topologies are made. Attempts to improve the classical three-loop topology are discussed. Despite the same open-loop structure, the classical three-loop autopilot shows distinct characteristics from a two-loop autopilot with PI compensator. Both the two-loop and three-loop topologies can stabilize a static unstable missile. However, the finite actuator resource is the crucial factor dominating autopilot function.
